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Tricking people into feeling like they are movingwhen they are not paying attention

Laura C. Trut.oiu!, Stephan Streuber, Betty J. Mohler, Jorg Schulte-Pelkum, and Heinrich H. BulthoffMax Planck Institute for Biological Cybernetics

AbstractVection refers to illusion of self motion in stationary obervers usu-ally by means of moving visual stimuli [Fischer and Kornmuller1930]. Linear vection naturally occurs when seated in a train andobserving another train on an adjacent track start moving. The verycompelling but brief illusion happens as observers are not payingparticular attention to the environment but are rather ”defocused”from the scene. We studied the effect of two visual attention taskson the perception of linear vection. The results show a significantdecrease in vection onset time with an attention task.

1 IntroductionVection, or the illusion of self-motion can be useful in a wide rangeof aplications: educational (driving and flight simulators) and evenentertainment (amusement park rides).

Figure 1: Tunnel projected onto a large screen virtual environment. The VE setupconsisted of an immersive large-screen display and a joystick (Saitek ST200). FourJVC D-ILA DLA-SX21S video projectors with a resolution of 1400 X 1050 pixelswere used to display visual stimuli on the front, sides, and floor of the a custom madecurved display.

There are likely many high-level cognitive effects that influencevection. In this paper we aim to investigate the role of attentionon the perception of vection. One previous study showed that anon-attended flow pattern determines vection direction when twodifferent optic flows are presented in the same depth plane [Ki-tazaki and Sato 2003]. In our study we used one optic flow patternand a concurrent visual attention task.2 Procedure and MethodEight paid volunteers participated in this experiment (balanced forgender). Participants sat on a chair at a distance of 3.5 meters fromthe curved projection screen which corresponds to a physical fieldof view of about 220 degrees horizontal by 165 degrees vertical, asillustrated in Figure 1. The visual stimuli consisted of a fully en-closed tunnel, and a set of 4 targets varying in shape and color. Five

!e-mail: laura.trutoiu@tuebingen.mpg.de

to eight of each of the four targets were placed directly in front ofthe observer in the same location on the bottom of the tunnel sepa-rated by a distance of 0-3 meters. Translational forward movementswere presented through this tunnel at a speed of 10m/s and for 30seconds. Participants were instructed to look straight ahead with-out following the moving targets. The experiment was programmedwith Virtools 4.0.The within subject design consisted of a total of three conditionswhere participants were asked to provide two different measures ofvection (vection onset and convincingness of vection). In two of theconditions an attention task was presented: either counting a spe-cific target (working memory condition) or pressing a button everytime they saw a specific target (visual attention condition). In thecontrol condition no attentional task was performed. Each partici-pant completed six blocks (2 repetitions of each condition). Every3 blocks were preceded by 2 practice trials. The entire experimenttook approximately 50 minutes to complete.

3 Results and ConclusionsAverage vection onset time for the control condition was 10.23 sec-onds, while for the two attentional task condition the onset timesdecreases to 8.25 seconds and 7.81 respectively (see Figure 2). Forvection onset analysis we removed the 13% of the trials where vec-tion was not experienced .

10.238.25 7.81

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Control Visual A!en"on Working Memory

Seconds Average Onset Time

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Figure 2: Average vection onset time for three different conditions of varying attentiondifficulty for eight subjects.

The results show a statistically significant difference (a paired sam-ple t test) between the working memory and the control condi-tion indicating improved vection with an attentional task (t=2.426,p=0.046).

AcknowledgementsThe authors wish to thank Prof. William B. Thompson, and Prof.John J. Rieser.

ReferencesFISCHER, M. H., AND KORNMULLER, A. E. 1930. Optokinetically induced motionperception and optokinetic nystagmus. Journal fur Psychologie und Neurologie,273–308.

KITAZAKI, M., AND SATO, T. 2003. Attentional modulation of self-motion percep-tion. Perception 32(4) 475 484.

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